【正确答案】 B

【答案解析】[听力原文]

Professor: You all know that a chain consists of links whether a jewelry chain or a food chain. The difference is that in a jewelry or metal chain, all the links are made of the same or similar material. In a food chain there are also links but food chains begin with plant life and end with an animal and each link is food for the next link. So, a food chain really shows how animals get their food. And, it shows how energy is given off at each level or link. Whenever there are finks, the more links there are in the food chain, the less energy the animal will get which is farther along the chain.
Student A: Why is there less energy? Does that really mean there is less food for animals farther along the chain?
Professor: Yes. That is because plants produce the food by using the sun"s energy to produce sugar or food from carbon dioxide and water, and that is why plants are called producers. Now, animals, on the other hand, are called consumers because they eat the plants or other animals and because they cannot make their own food.
Student B: But, there are some animals that only eat animals, some that only eat plants and some that eat both.
Professor: That"s absolutely correct. That is why there are different types of consumers. Plant eaters are called herbivores (plant eater). Animal eaters are called carnivores, and animals, and people, for that matter, who eat both plants and animals, are called omnivores. There is a third part of the chain I didn"t tell you about: the decomposers.
Student A: How are the decomposers involved in the food chain? Do they eat the plant or animal?
Professor: No, they don"t eat either the plant or animal. What they do, is to feed upon decaying matter and to release material, or nutrients, they get from it back into the soil. The plants absorb them so they can begin the food cycle again.
Now, I want to talk a little more about energy loss and the links of the chain and how food is passed from one link to another. When a herbivore eats, most of the energy it gets from plant food is used to maintain its life.
Student A: I really don"t understand. Are you saying that animals don"t store a lot of energy in their body and then as they are a link in the food chain they don"t have too much energy to pass on to the next animal?
Professor: Exactly. That is why the more the links in the food chain, the less energy there is to pass on with each rink. And that is why there are usually only four or five links in each food chain.
Student B: Well, if an animal needs more energy, can it be part of more than one food chain?
Professor: Yes. That is exactly what happens.
Think of a food chain as a pathway. A single path is where animals get their food. But when they need more than a single pathway can provide, they go to other pathways. Like this, animals are usually part of more than one chain and when that happens, animals eat more than one kind of food so they have enough both of food and energy. The chains, then, are interconnected and are part of what is called a "food web."
Now, the food web is made up of many single pathways and a web permits more animals to find food. But you have to remember that animals living in the tropics may have different requirements from animals living in the arctic, and the food web for each ecosystem will probably be different. The same will be true for marine animals and those living by ponds—their food webs will also be different.
Student B: Can you give us an example?
Student A: Could you give us a simple example of a food chain?
Professor: Sure. Let"s take, for example, the ecosystem of a rainforest and a food chain that might exist. You all know that under the canopy of the rainforest, there are lots of small plants that have lots of nutrients. There are mosses and grass and plants like mushrooms. And there are shrubs, too. Sometimes the trees forming the canopy, or roof, of the rainforest are coniferous and drop their cones to the floor of the forest. These would be the producers plants which produce energy.
Student A: Then little animals, squirrels and mice, and maybe birds, eat the plants?
Student B: Yahh... according to what I read, they are primary consumers because they are the first animals or links in the chain.
Professor: Yes. The larger animals or birds eat the smaller and they are secondary consumers. Finally large birds like vultures may eat the small thrushes and as the third rink, they are called tertiary consumers. Bears eating fish from streams might also be an example of a tertiary consumer. This is an example of a single chain. When animals need more food than the one chain can offer, they participate in another chain and the second chain becomes part of a food web.

[解析] 教授通过珠宝项链和金属链引入了讨论的中心话题：食物链，之后的整个讨论都围绕这个话题展开。

【正确答案】 A

【答案解析】[解析] 教授将一条食物链比作一条单一路径，动物们需要有多条路径来获得足够的食物，这样就构成了食物网。这时，学生们让教授举一个单一食物链的例子，教授就列举了热带雨林中食物链的例子进行解释说明(the ecosystems of a rainforest and a food chain that might exist)。

【正确答案】 B、C

【答案解析】[解析] 教授在讲述分解者做出的贡献时这样说道：What they do, is to feed upon decaying matter and to release material, or nutrients, they get from it back into the soil. B选项对应这句话中的feed upon decaying matter；C选项对应其中的release material, or nutrients, they get from it back into the soil。

【正确答案】 B、D、E

【答案解析】[解析] 由讲座中的That is because plants produce the food by using the sun"s energy to produce sugar or food from carbon dioxide and water可知B选项正确；由Like this, animals are usually part of more than one chain...they have enough both of food and energy可知D选项正确； Now, animals, on the other hand, are called consumers because they eat the plants or other animals可知E选项正确。

【正确答案】 B

【答案解析】[听力原文]
Professor: In a food chain there are also links but food chains begin with plant life and end with an animal and each link is food for the next link. So, a food chain really shows how animals get their food. And, it shows how energy is given off at each level or link. Whenever there are links, the more links there are in the food chain, the less energy the animal will get which is farther along the chain.
What does the professor mean when he says this:
...the more links that are in the food chain, the less energy the animal will get which is farther along the chain.

[解析] 教授指出食物链中越末端的动物吸收的能量就越少，这是因为它从上一环节吸收的能量少，而这又归结于上一环节本身储存的能量也不多。B选项与教授所说话语的含义相吻合。

【正确答案】 C

【答案解析】[听力原文]
Student A: Then little animals, squirrels, and mice, and maybe birds, eat the plants?
Student B: Yahh... according to what I read, they are primary consumers because they are the first animals or links in the chain.
What can be inferred about the students?

[解析] 解答本题需要准确把握学生的语气，女生是疑问的语气，而男生是用肯定的语气描述了初级消费者，接着教授对这些说法进行了肯定的回复。可见C选项是正确答案。